Forward Monitoring System

ABSTRACT

As a front monitoring system of a vehicle with strict restrictions on device arrangement, in a case where one or a plurality of external sensors are installed, an exit wave emitted from the external sensors and reflected by a structural object inside the vehicle is prevented from reentering the external sensor, and erroneous detection of an object is suppressed. As a front monitoring system therefor, an external sensor that is mounted inside a vehicle, emits an exit wave toward a front of the vehicle, and acquires a reflected wave entering the external sensor as a detection signal, and a removing means that removes the exit wave emitted by the external sensor and incident on a structural object installed inside the vehicle in a specific direction, particularly at an incident angle larger than a predetermined angle are provided.

TECHNICAL FIELD

The present invention relates to a front monitoring system related totraffic.

BACKGROUND ART

In a railway driverless system and a railway driving support system, asystem that avoids a collision between a train and an object bymonitoring the front of the train and detecting the object that mayhinder the traveling of the train is indispensable. In the case of atrain, remote monitoring of the front of the train is required forreasons such as a long braking distance, but near monitoring of theperiphery of the train is also required to avoid collision with anobject at the periphery of the train at the time of starting the trainor the like.

As a near monitoring means at the periphery of the train, it iseffective to use LiDAR that detects an object by scanning a wide areawith a laser and performing laser ranging. In a case where LiDAR ismounted on a train, installation on an existing train is assumed. If theLiDAR is installed outside the vehicle, there is a concern that thelifespan of the LiDAR is shortened due to environmental factors such asrain and wind, and the reliability of the train front monitoring systemusing the LiDAR is lowered. Therefore, the LiDAR used for frontmonitoring has a high possibility of being installed inside the train.

When the LiDAR is installed in a train, there is a possibility that alaser emitted by the LiDAR is reflected by an in-vehicle structuralobject or the like and re-enters the own LiDAR. Furthermore, a system inwhich a plurality of LiDARs are installed to secure a wide field of viewis considered, but in the case of such a system, there is still apossibility that a laser emitted from a certain LiDAR is reflected by anin-vehicle structural object or the like and enters another LiDAR.

Due to the laser that is reflected by the in-vehicle structural objector the like and incident on the LiDAR, a point group that does notoriginally exist appears in the data of point group acquired by theLiDAR. Since front monitoring and object detection are performed fromthe acquired point group, there is a risk that erroneous detection of anobject occurs due to such a point group that does not originally exist.

Since the train mounted with the front monitoring system performs thebrake operation determination based on the detection result of theobject, an erroneous brake command is sent if the object is erroneouslydetected, which may lead to a decrease in the transportation efficiencyof the train. Therefore, the laser reflected by the in-vehiclestructural object needs to be removed as it causes erroneous detectionof an object.

Therefore, PTL 1 proposes a method of preventing erroneous detection ofan object due to the installation of a plurality of LiDARs by installinga division structure between a plurality of LiDARs having differentwavelengths and causing only a laser light having a specific wavelengthto enter the LiDAR by an optical filter so that no other LiDAR laserenters.

In addition, PTL 2 proposes a technique in which an optical filter ismounted inside a LiDAR to limit a range of an incident angle of a laserwith respect to a laser light receiving portion and exclude a laseroutside the range as stray light after grasping an incident direction ofthe laser when a laser emitted from the LiDAR is reflected in asurrounding environment and normally incident on the LiDAR. Thus, amongthe lasers emitted by the LiDAR, only the laser reflected by an objectother than the LiDAR is collected, and stray light is excluded.

CITATION LIST Patent Literature

-   PTL 1: JP 2018-511056 A-   PTL 2: JP 2012-154806 A

SUMMARY OF INVENTION Technical Problem

In the method described in PTL 1, a plurality of LiDARs need to bearranged in spaces completely separated by a division structure, andthus it is not easy to implement it on a train in which restrictions inthe arrangement of devices installed in the vehicle is strict. Inaddition, it is difficult to prevent a phenomenon that erroneousdetection occurs when a laser that it has emitted is reflected by anin-vehicle structural object and entered to the LiDAR again.

Furthermore, in the method described in PTL 2, a direction of a lasernormally entering a light receiving portion in the LiDAR is grasped inadvance, and a stray light laser that enters at an angle different fromthe laser is removed by an optical filter. However, when another laseremitted by a LiDAR different from a specific LiDAR is reflected by thein-vehicle structural object, there is a possibility that the laser mayenter the light receiving portion at an incident angle similar to thatof the specific laser, and thus it is difficult to remove the laser asstray light by the optical filter.

Furthermore, since the method described in PTL 2 is based on a LiDARincorporating a special optical filter, it is difficult to use themethod described in PTL 2 for a LiDAR not mounted with this opticalfilter.

As described above, in a case where an external sensor using one or aplurality of reflected waves by, for example, LiDAR is installed on atrain in which restrictions in the arrangement of the devices arerestrict, a phenomenon in which an unintended point group coexists inthe point group data acquired by the external sensor occurs due to theexit wave emitted by the external sensor being reflected by thein-vehicle structural object and then incident on the external sensor.

An object of the present invention is to provide a front monitoringsystem that prevents this phenomenon caused by an external sensor,thereby suppressing erroneous detection caused by this phenomenon.

Solution to Problem

In order to solve such a problem, a front monitoring system according tothe present invention includes an external sensor that is mounted insidea vehicle, emits an exit wave toward a front of the vehicle, andacquires a reflected wave entering the external sensor as a detectionsignal, and includes a removing means that removes the exit wave emittedby the external sensor and incident on a structural object installedinside the vehicle in a specific direction, particularly at an incidentangle larger than a predetermined angle.

Advantageous Effects of Invention

According to the present invention, in a case where one or a pluralityof external sensors is installed in a vehicle with strict devicearrangement restrictions, it is possible to prevent a phenomenon inwhich an unintended point group coexist in point group data acquired bythe external sensor due to an exit wave emitted by the external sensorbeing reflected by a structural object installed inside the vehicle andthen incident on the external sensor itself. As a result, erroneousdetection caused by such a phenomenon can be significantly suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an outline of a means for removingreflected exit wave according to the present invention.

FIG. 2 is a diagram illustrating an example of a configuration of afront monitoring system according to a first embodiment.

FIG. 3 is a three-view diagram illustrating an arrangement relationshipbetween a first external sensor and a plate.

FIG. 4 is a top view illustrating a positional relationship of the firstexternal sensor, an in-vehicle structural object, and the plate.

FIG. 5 is a side view illustrating a positional relationship of thefirst external sensor, the in-vehicle structural object, and the platein two cross sections.

FIG. 6 is a diagram illustrating an example of a configuration of afront monitoring system according to a second embodiment.

FIG. 7 is a diagram illustrating a method of removing an erroneouslyentered point group in a third embodiment.

FIG. 8 is a diagram illustrating a flowchart for point group exclusionaccording to the third embodiment.

FIG. 9 is a diagram illustrating a point group acquired by a secondexternal sensor in a fourth embodiment.

FIG. 10 is a diagram illustrating a flowchart for point group exclusionaccording to the fourth embodiment.

FIG. 11 is a diagram illustrating a point group acquired by the secondexternal sensor when irradiation of the exit wave from the firstexternal sensor is stopped.

FIG. 12 is a diagram illustrating a state in which a point groupreceived by the second external sensor remains by the exit wave from thefirst external sensor.

FIG. 13 is a diagram illustrating a point group excluding all pointgroups derived from an exit wave emitted by the first external sensor.

FIG. 14 is a diagram illustrating an example of arrangement in a casewhere all of the first external sensor, the second external sensor, andthe in-vehicle structural object are mounted on different vehicles in afifth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described as modes for implementing thepresent invention with reference to the drawings. In addition, thefollowing embodiments are examples embodying the present invention, andare not intended to limit the technical scope of the present invention.

In describing each embodiment according to the present invention, anoutline of a method for removing an unnecessary exit wave for preventingerroneous detection will be described in common in each embodiment.

FIG. 1 is a diagram illustrating an outline of a means for removing areflected exit wave according to the present invention, and illustratesan outline of a means 50 for removing an exit wave emitted by a firstexternal sensor 10 and reflected by an in-vehicle structural object 30.

The exit wave emitted from the first external sensor 10 is divided intoan exit wave 101 that is transmitted and an exit wave 102 that is nottransmitted but reflected with respect to the in-vehicle structuralobject 30.

Here, the first external sensor 10 is a sensor that performs distancemeasurement using a reflected wave. For example, there are LiDAR fordetecting an object by scanning a wide area with a laser and performinglaser ranging, millimeter wave radar for detecting a surrounding objectby emitting a radio wave in a millimeter wave band, and the like.

The exit wave to be used is a wave emitted from the first externalsensor 10 and used for distance measurement. For example, there arelaser light and radio waves in a millimeter wave band.

The in-vehicle structural object 30 is a structural object constitutingthe interior of the vehicle. Examples thereof include, for example, awindshield and a metallic wall surface. The exit wave 102 reflected byin-vehicle structural object 30 advances along optical path 103.Furthermore, examples of the vehicle include, for example, a railwayvehicle and an automobile.

Since the exit wave 102 that becomes a reflected wave is reflected bythe in-vehicle structural object 30 and incident on the first externalsensor 10 again, there is a possibility that a point group that does notoriginally exist is acquired from the exit wave 102.

Furthermore, in a case where the second external sensor 20 is installed,there is a possibility that the exit wave 102 enters the second externalsensor 20, and a point group that does not originally exist is acquiredfrom the exit wave 102. The second external sensor 20 is a sensor thatperforms distance measurement using a reflected wave, similarly to thefirst external sensor 10. For example, there are LiDAR that emits aplurality of lasers to measure the surrounding distance, millimeter waveradar that emits radio waves in a millimeter wave band to detectsurrounding objects, and the like.

Therefore, in order not to acquire a point group that does notoriginally exist, it is necessary to prevent the exit wave 102 fromentering the first external sensor 10 or the second external sensor 20.

As means for this, a method of physically blocking the exit wave 102 byinserting a plate or the like to block the optical path 103 of the exitwave 102, or a method of analyzing the point group data acquired by thesecond external sensor 20 and removing the point group derived from theexit wave 102 by software processing can be considered.

Hereinafter, a method of physically blocking and a method of removing bysoftware processing will be described with the embodiments.

First Embodiment

A first embodiment is an example of a method of physically blocking thereflected unnecessary exit wave 102.

FIG. 2 is a diagram illustrating an example of a configuration of afront monitoring system according to the first embodiment. This is anexample in which a plate 51 having a low reflectance is installed on thefront surface side of the first external sensor 10 in order to block theexit wave 102 reflected by the in-vehicle structural object 30 of theexit wave emitted by the first external sensor 10.

In FIG. 2 , the exit wave in a case where the incident angle to thein-vehicle structural object 30 is larger than or equal to apredetermined angle 4A of the exit wave emitted by the first externalsensor 10 is regarded as the exit wave 102 reflected by the in-vehiclestructural object 30. For example, when the in-vehicle structural object30 is a windshield, the predetermined angle 4A may be a critical anglein a phenomenon where total reflection occurs at a boundary surfacebetween the windshield and the outside air without passing through thewindshield.

In this manner, the exit wave having an incident angle with respect tothe in-vehicle structural object 30 of larger than or equal to thepredetermined angle 4A is blocked by the plate 51 using thepredetermined angle 4A. As a result, the exit wave 102 reflected withoutbeing transmitted through the in-vehicle structural object 30 can beblocked, and the exit wave 102 can be prevented from entering the firstexternal sensor 10 or the second external sensor 20 while maximallyusing the exit wave 101 transmitted through the in-vehicle structuralobject 30 useful for front monitoring, Therefore, in front monitoring,erroneous detection caused by acquiring a point group that is derivedfrom the exit wave 102 and does not originally exist can be reduced.Note that the incident angle is an angle formed by the incidentdirection and the normal line of the boundary surface.

Next, an example of the arrangement, shape, and dimension of the plate51 for blocking the exit wave 102 will be specifically described withreference to FIGS. 3, 4, and 5 .

FIG. 3 is a trihedral figure illustrating an arrangement relationshipbetween the first external sensor 10 and the plate 51, and illustratesan arrangement of the plate 51 installed on the front surface of thefirst external sensor 10 and a dimension of the plate 51. Here, FIG. 3is illustrated by a third angle system.

In FIG. 3 , reference numeral 105 denotes a horizontal field of view(FoV) (hereinafter, “horizontal FoV” is referred to as a “horizontalviewing angle”) of the first external sensor 10, and reference numeral106 denotes a vertical field of view (FoV) (hereinafter, referred to asa “vertical viewing angle”) of the first external sensor 10. A centerline 107 is a straight line in which a fan shape representing thehorizontal viewing angle (105) and a fan shape representing the verticalviewing angle (106) intersect, and the other center lines 108 and 109are straight lines perpendicular to the center line 107.

The condition that the dimension of the plate 51 should satisfy to blockthe exit wave 102 is determined by the distance 516 between the firstexternal sensor 10 and the plate 51, the horizontal viewing angle (105),the vertical viewing angle (106), the refractive index of the in-vehiclestructural object 30, and the positional relationship between thein-vehicle structural object 30 and the first external sensor 10. Here,the dimension of the plate 51 is defined by the distance with the centerline 108 and the center line 109, and as illustrated in FIG. 3 , is thedistance 512, the distance 513, the distance 514, and the distance 515.

Hereinafter, an example of a method of calculating a condition that thedimension from the distance 512 to the distance 515 should satisfy willbe described with reference to FIGS. 4 and 5 .

FIG. 4 is a top view illustrating a positional relationship of the firstexternal sensor 10, the in-vehicle structural object 30, and the plate51, where a fan shape constituting the horizontal viewing angle (105) isparallel to the plane of drawing. Hereinafter, dimensional conditions(distance 512 to distance 515) of the plate 51 for excluding an exitwave having an incident angle with respect to the in-vehicle structuralobject 30 of larger than or equal to the predetermined angle 4A from theexit wave 102 emitted by the first external sensor 10 will be described.

However, for the sake of generalization, the in-vehicle structuralobject 30 is assumed to be inclined at a certain angle and not parallelto the plate 51. As illustrated in FIG. 5 , an angle formed by thein-vehicle structural object 30 and a plane 301 parallel to thehorizontal viewing angle (105) is 4B. Thus, by setting the angle 4B, thefirst embodiment can also be applied to a vehicle in which the angle 4Btakes a value other than 90 °, such as a railway vehicle or a passengercar.

In order to obtain the dimensional condition from the distance 512 tothe distance 515, an A-A cross-sectional view 517 and a B-Bcross-sectional view 518 illustrated in FIG. 5 are used in addition toFIG. 4 . FIG. 5 is a side view (A-A cross-sectional view 517 and B-Bcross-sectional view 518) illustrating a positional relationship of thefirst external sensor 10, the in-vehicle structural object 30, and theplate 51 in two cross sections.

First, the A-A cross-sectional view 517 is a cross-sectional view of theincident angle of the exit wave 102 emitted from the first externalsensor 10 with respect to the in-vehicle structural object 30 within arange in which the incident angle in the horizontal direction is smallerthan the predetermined angle 4A (FIG. 4 ) when a plane parallel to thehorizontal viewing angle (105) is assumed as a horizontal plane.

As illustrated in FIG. 4 , the distance 513 in the horizontal directionis set to a value that satisfies, of the exit wave 102 emitted from thefirst external sensor 10, not blocking the exit wave having an incidentangle with respect to the in-vehicle structural object 30 of smallerthan the predetermined angle 4A, and blocking the exit wave having anincident angle of larger than or equal to the predetermined angle 4A.

In the A-A cross-sectional view 517 illustrated in FIG. 5 , when a planeparallel to the vertical viewing angle (106) is assumed as a verticalplane, there is a possibility that the incident angle in the verticaldirection becomes larger than or equal to the predetermined angle 4A asin an exit wave 102 in the A-A cross-sectional view 517.

Therefore, the distance 515 in the vertical direction is a value thatsatisfies, of the exit wave 102 emitted from the first external sensor10, not blocking the exit wave 102 having an incident angle in the A-Across-sectional view 517 of smaller than the predetermined angle 4A, andblocking the exit wave 102 having an incident angle in the A-Across-sectional view 517 of larger than or equal to the predeterminedangle 4A. Furthermore, distance 514 in the vertical direction is set toa value that satisfies blocking of all exit waves 102 having an incidentangle in the A-A cross-sectional view 517 of larger than or equal to thepredetermined angle 4A.

Next, the B-B cross-sectional view 518 is a cross-sectional view of theincident angle of the exit wave 102 emitted from the first externalsensor 10 with respect to the in-vehicle structural object 30 within arange in which the incident angle in the horizontal direction is largerthan or equal to the predetermined angle 4A (FIG. 4 ) when a planeparallel to the horizontal viewing angle (105) is assumed as ahorizontal plane.

As illustrated in FIG. 4 , the distance 512 in the horizontal directionis set to a value that satisfies blocking of all exit waves havingincident angles with respect to the in-vehicle structural object 30 oflarger than or equal to the predetermined angle 4A of the exit waves 102emitted from the first external sensor 10.

In the B-B cross-sectional view 518 illustrated in FIG. 5 , all of theexit waves 102 emitted from the first external sensor 10 are reflectedby the in-vehicle structural object 30. Therefore, the distance 514 inthe vertical direction is set to a value that satisfies blocking of allexit waves 102 in the B-B cross-sectional view 518.

The plate 51 having the dimension determined by the above method isinstalled between the first external sensor 10 and the in-vehiclestructural object 30. As a result, among the exit waves 102 emitted bythe first external sensor 10, the exit wave 102 reflected by thein-vehicle structural object 30 can be removed while maximally using theexit wave 101 transmitted through the in-vehicle structural object 30,and erroneous detection of the external sensor from the exit wave 102can be reduced. Note that the same applies to a case where therelationship between the emission and incidence of the first externalsensor 10 and the second external sensor 20 is reversed, and the plate51 is arranged on the front surface side of the second external sensor20.

Second Embodiment

A second embodiment is another example of a method of physicallyblocking the reflected unnecessary exit wave 102. However, the secondembodiment is a method of providing a margin in the arrangement of theplate used at the time of physical blocking by imposing somerestrictions on the arrangement of the first external sensor 10 and thesecond external sensor 20.

FIG. 6 is a diagram illustrating an example of the configuration of thefront monitoring system according to the second embodiment, andillustrates the arrangement of the first external sensor 10, the secondexternal sensor 20, and the plate 52 for blocking the exit wave 102reflected by the in-vehicle structural object 30.

The center line 207 is a straight line in which a fan shape representingthe horizontal viewing angle (205) of the second external sensor 20 anda fan shape representing the vertical viewing angle (206, not shown)intersect.

In the second embodiment, the distance between the center line 107 andthe center line 207 is defined as a distance 522, and the plate 52 isassumed to be on a plane parallel to the vertical viewing angle (106,not shown) of the first external sensor 10.

Furthermore, as illustrated in FIG. 6 , among the exit waves emittedfrom the first external sensor 10, a point where the exit wave 102 Hhaving the largest incident angle with respect to the in-vehiclestructural object 30 collides with the in-vehicle structural object 30and is closer to the second external sensor 20 is defined as a firstreflection point 110H. Similarly, among the exit waves emitted from thesecond external sensor 20, a point where the exit wave 202H having thelargest incident angle with respect to the in-vehicle structural object30 collides with the in-vehicle structural object 30 and is closer tothe first external sensor 10 is defined as a second reflection point210H. A distance between the first reflection point 110H and the secondreflection point 210H is defined as a distance 521.

At this time, the first external sensor 10, the first reflection point110H, the plate 52, the second reflection point 210H, and the secondexternal sensor 20 are lined in this order, and the distance 522 is setsuch that the distance 521 is a value larger than 0. Then, as long asthe dimension of the plate 52 is set to block all of the exit waves 102emitted from the first external sensor 10, reflected by the in-vehiclestructural object 30, and incident on the second external sensor 20 andthe exit waves 202 emitted from the second external sensor 20, reflectedby the in-vehicle structural object 30, and incident on the firstexternal sensor 10, the plate 52 may be placed anywhere within thesection of the distance 521.

If the distance between the first external sensor 10 and the secondexternal sensor 20 can be appropriately set by the above method, itbecomes possible to remove only the exit wave reflected by thein-vehicle structural object 30 without strictly determining thedimension and arrangement of the plate 52. As a result, the dimensionand positioning cost can be reduced while having the same performance asin the first embodiment other than the arrangement of the externalsensors.

Third Embodiment

A third embodiment is an example of a method of removing an exit waveemitted from the first external sensor 10 and reflected by thein-vehicle structural object 30 by software processing withoutphysically shielding the exit wave with a plate or the like.

FIG. 7 is a diagram illustrating a method of removing an erroneouslyentered point group in the third embodiment. It is a method of removingthe point group erroneously entered from the first external sensor 10among the point groups obtained by the second external sensor 20 byusing the positional relationship of the first external sensor 10, thesecond external sensor 20, and the in-vehicle structural object 30.

In FIG. 7 , since the exit wave 102 emitted from the first externalsensor 10 and reflected by the in-vehicle structural object 30 is notshielded in the middle, some of the exit waves 102 are reflected by thein-vehicle structural object 30 and incident on the second externalsensor 20. Therefore, among the exit waves 102 reflected by thein-vehicle structural object 30, those entering the second externalsensor 20 are referred to as exit waves 531, and those not entering thesecond external sensor 20 are referred to as exit waves 532.

Since the incident angle of the exit wave 531 incident on the secondexternal sensor 20 also has an angle width, the maximum incident angleis set to 6B and the minimum incident angle is set to 6A at the incidentangle of the exit wave 531 to the second external sensor 20. Both theminimum incident angle 6A and the maximum incident angle 6B can becalculated based on the geometric arrangement of the first externalsensor 10, the second external sensor 20, and the in-vehicle structuralobject 30 and the refractive index of the in-vehicle structural object30.

In view of this, if the point group of larger than or equal to theminimum incident angle 6A and smaller than or equal to the maximumincident angle 6B is removed with respect to the point group acquired bythe second external sensor 20, an unnecessary point group derived fromthe exit wave 102 emitted from the first external sensor 10 can beremoved.

Next, software processing for removing a point group of larger than orequal to the minimum incident angle 6A and smaller than or equal to themaximum incident angle 6B from the point group obtained by the secondexternal sensor 20 will be described.

FIG. 8 is a diagram illustrating a flowchart for point group exclusionaccording to the third embodiment. An execution subject of each stepconstituting this flowchart is a processing device (not illustrated)included in the front monitoring system according to the presentinvention, but the description of the execution subject is omittedbelow.

In step 101 (S101), the point group data derived from the exit waveincident on the second external sensor 20 is acquired. The point groupdata includes a point group derived from the exit wave emitted by thesecond external sensor 20 itself and a point group derived from the exitwave emitted by the first external sensor 10, reflected by thein-vehicle structural object 30, and incident on the second externalsensor 20.

Step 102 (S102) is a start step in performing the processing on each ofall the acquired point groups.

When determined in step 103 (S103) that the incident angle 60 of theexit wave is larger than or equal to the minimum incident angle 6A forthe point acquired from the point group to be processed (YES), theprocess proceeds to step 104 (S104). On the other hand, when determinedthat the incident angle 60 of the exit wave is smaller than the minimumincident angle 6A (NO), the process proceeds to step 111 (S111) .

When determined in step 104 (S104) that the incident angle 60 of theexit wave satisfies the condition of smaller than or equal to themaximum incident angle 6B (YES), this point satisfies the incident angle60 being larger than or equal to the minimum incident angle 6A andsmaller than or equal to the maximum incident angle 6B, and thus theprocess proceeds to step 105 (S105). On the other hand, when determinedthat the incident angle 60 of the exit wave is greater than the maximumincident angle 6B (NO), the process proceeds to step 111 (S111) .

In step 105 (S105), the acquired points are regarded as corresponding tothe point group derived from the exit wave emitted by the first externalsensor 10 and excluded.

In step 106 (S106), the process returns to step 102 (S102) to executethe point group processing loop until the processing on all the pointgroups is completed, and the process proceeds to step 107 (S107) afterthe point group processing loop is terminated.

In step 107 (S107), the remaining point groups excluding the point atwhich the incident angle 60 of the exit wave is larger than or equal tothe minimum incident angle 6A and smaller than or equal to the maximumincident angle 6B are output as data of a point group necessary formonitoring.

In step 111 (S111) , the acquired points are held as data of point groupnecessary for monitoring.

In addition, the processing flow from step 101 (S101) to step 111 (S111)is executed each time the second external sensor 20 acquires a pointgroup.

As described above, in the third embodiment, if the positionalrelationship of the first external sensor 10, the second external sensor20, and the in-vehicle structural object 30 and the refractive index ofthe in-vehicle structural object 30 are known, the point group derivedfrom the exit wave reflected by the in-vehicle structural object 30 andincident on the second external sensor 20 can be removed by software. Asa result, the erroneous detection in front monitoring performed in thepost-stage processing can be reduced. In addition, by providing theupper limit value for the incident angle to be excluded, the point groupcan be prevented from being excluded more than necessary, andperformance deterioration of front monitoring by the external sensor canbe suppressed. Of course, the same applies to a case where therelationship between the emission and incidence of the first externalsensor 10 and the second external sensor 20 is reversed.

Fourth Embodiment

A fourth embodiment is another example of a method of removing an exitwave emitted from the first external sensor 10 and reflected by thein-vehicle structural object 30 by software processing withoutphysically shielding the exit wave with a plate or the like.

FIG. 9 is a diagram illustrating a point group acquired by the secondexternal sensor in the fourth embodiment. A point group 540 a acquiredby the second external sensor 20 based on the exit wave that has enteredthe second external sensor 20 is illustrated. The point group 540 aincludes a point group 541 derived from an exit wave emitted from thesecond external sensor 20, normally reflected by an object in front ofthe vehicle, and entered to the second external sensor 20, and a pointgroup 542 derived from an exit wave emitted from the first externalsensor 10, reflected by the in-vehicle structural object 30, and enteredto the second external sensor 20. Among them, the point group 542 is apoint group that does not originally exist, and thus needs to beremoved.

The fourth embodiment is a method of removing the point group 542derived from the exit wave emitted by the first external sensor 10 bycomparing the point group 540 a (FIG. 9 ) acquired by the secondexternal sensor 20 when the first external sensor 10 is emitting theexit wave and the point group 540 b (FIG. 11 ) acquired by the secondexternal sensor 20 when the first external sensor 10 is not emitting theexit wave to remove the point group 542.

FIG. 10 is a diagram illustrating a flowchart for point group exclusionaccording to the fourth embodiment. An execution subject of each stepconstituting this flowchart is a processing device (not illustrated)included in the front monitoring system according to the presentinvention, but the description of the execution subject is omittedbelow.

In step 201 (S201), the point group data 540 a is acquired from thesecond external sensor 20.

In step 202 (S202), the irradiation of the exit wave from the firstexternal sensor 10 is stopped.

In step 203 (S203), the point group data 540 b is acquired from thesecond external sensor 20 in a state where the first external sensor 10is not emitting the exit wave. Here, FIG. 11 is a diagram illustrating apoint group 540 b acquired by the second external sensor 20 when theirradiation of the exit wave from the first external sensor 10 isstopped. As illustrated in FIG. 11 , the point group 543 derived fromthe exit wave emitted by the first external sensor 10 is not acquired,and only the point group 541 derived from the exit wave emitted by thesecond external sensor 20 is acquired.

In step 204 (S204), points present in the point group data 540 b areexcluded from the point group data 540 a. FIG. 12 is a diagramillustrating a state in which the point group received by the secondexternal sensor 20 remains by the exit wave from the first externalsensor 10 due to the exclusion. That is, only the point group 544derived from the exit wave emitted by the first external sensor 10 canbe extracted.

In step 205 (S205), the point group remaining after the exclusion instep 204 (S204) is set as the point group 544.

In step 206 (S206), the minimum incident angle 7A and the maximumincident angle 7B are calculated from the incident angle with respect tothe second external sensor 20 for each of the exit waves correspondingto the point group 544.

In step 207 (S207), the point group 540 c is acquired by removing thepoint group 544 derived from the exit wave entering the second externalsensor 20 at the incident angle of larger than or equal to the minimumincident angle 7A and smaller than or equal to the maximum incidentangle 7B from the point group data 540 a. FIG. 13 is a diagramillustrating the point group 540 c acquired in this manner. Since allthe point groups derived from the exit wave emitted by the firstexternal sensor 10 are included in the exit wave entering the secondexternal sensor 20 at larger than or equal to the minimum incident angle7A and smaller than or equal to the maximum incident angle 7B, all thepoint groups derived from the exit wave emitted by the first externalsensor 10 are excluded from the point group 540 c.

Finally, in step 208 (S208), the point group 540 c is output to, forexample, a front monitoring algorithm or the like using an externalsensor.

As described above, in the fourth embodiment, the point group derivedfrom the exit wave emitted by the first external sensor 10 can beremoved from the point group acquired by the second external sensor 20without grasping the positional relationship of the first externalsensor 10, the second external sensor 20, the in-vehicle structuralobject 30, and the like in advance. Of course, the same applies to acase where the relationship between the emission and incidence of thefirst external sensor 10 and the second external sensor 20 is reversed.

Fifth Embodiment

In the fourth embodiment described above, when removing the point groupderived from the exit wave emitted by the first external sensor 10 fromthe point group acquired by the second external sensor 20, thepositional relationship of the first external sensor 10, the secondexternal sensor 20, the in-vehicle structural object 30, and the likedoes not need to be grasped in advance.

Therefore, the method of the fourth embodiment can also be applied to acase where at least one of the first external sensor 10, the secondexternal sensor 20, and the in-vehicle structural object 30 is mountedon a different vehicle, and the positional relationship of the firstexternal sensor 10, the second external sensor 20, and the in-vehiclestructural object 30 is unknown.

A fifth embodiment is an example in which the method of the fourthembodiment is applied to a case where each of the first external sensor10, the second external sensor 20, and the in-vehicle structural object30 are mounted on different vehicles.

FIG. 14 is a diagram illustrating an example of arrangement in a casewhere each of the first external sensor 10, the second external sensor20, and the in-vehicle structural object 30 are mounted on differentvehicles in the fifth embodiment.

As illustrated in FIG. 14 , the first external sensor 10 is mounted on avehicle 801, the second external sensor 20 is mounted on a vehicle 802different from the vehicle 801, and the in-vehicle structural object 30is mounted on a vehicle 803 different from the vehicle 801 and thevehicle 802. In addition, the vehicle 801 and the vehicle 803, and thevehicle 802 and the vehicle 803 face each other.

In this arrangement, the exit wave emitted by the first external sensor10 is divided into an exit wave 102 reflected by the in-vehiclestructural object 30 and an exit wave 101 not reflected by thein-vehicle structural object 30, and furthermore, the exit wave 102 isdivided into an exit wave 531 entering the second external sensor 20 andan exit wave 532 not entering the second external sensor 20.

The above configuration is similar in arrangement to the fourthembodiment other than that the vehicle on which each of the firstexternal sensor 10, the second external sensor 20, and the in-vehiclestructural object 30 is mounted is different, and thus the method of thefourth embodiment described above can be used. Thus, the point groupderived from the exit wave emitted by the first external sensor 10 canbe removed from the point group acquired by the second external sensor20.

Sixth Embodiment

The above fourth embodiment is a method of comparing a case where thefirst external sensor 10 is emitting the exit wave and a case where thefirst external sensor 10 is not emitting the exit wave to extract thepoint group 544 (FIG. 12 ) derived from the first external sensor 10,and calculate the minimum incident angle 7A and the maximum incidentangle 7B.

A sixth embodiment is a method of calculating a direction of enteringthe second external sensor 20 as an excluding direction from an exitwave corresponding to each point constituting the point group 544, andremoving the point group corresponding to the excluding direction fromthe point group acquired by the second external sensor 20.

As a result, the point group derived from the exit wave emitted by thefirst external sensor 10 can be removed from the point group acquired bythe second external sensor 20. Of course, the same applies to a casewhere the relationship between the emission and incidence of the firstexternal sensor 10 and the second external sensor 20 is reversed.

Seventh Embodiment

The methods of the first to sixth embodiments described above areembodiments in which the application target is specified as a vehicle.

A seventh embodiment is a mode in which the methods of the first tosixth embodiments described above are applied not only to vehicles butalso to ground facilities for traffic route peripheral monitoringarranged along a railroad, a road, or the like.

Specifically, if the vehicle is replaced with the ground facility andthe in-vehicle structural object 30 is replaced with an in-groundfacility structural object in each of the above embodiments, the methodsof the first to sixth embodiments can be applied to the ground facility.In the seventh embodiment, the in-ground facility structural object is astructural object that is installed in the ground facility and reflectsan exit wave emitted by the first external sensor 10, and correspondsto, for example, glass installed to protect the first external sensor 10from rain and wind.

REFERENCE SIGNS LIST

-   1 front monitoring system-   10 first external sensor-   20 second external sensor-   30 in-vehicle structural object-   4A predetermined angle-   50 means for blocking exit wave of first external sensor reflected    by in-vehicle structural object-   51 plate (first embodiment)-   52 plate (second embodiment)-   6A minimum incident angle (third embodiment)-   6B maximum incident angle (third embodiment)-   7A minimum incident angle (fourth embodiment)-   7B maximum incident angle (fourth embodiment)-   101, 102, 201, 202, 531, 532 exit wave-   103, 203 reflected wave-   105 horizontal viewing angle (FoV)-   106 vertical viewing angle (FoV)-   107 to 109, 207 center line-   110H, 210H reflection point-   301 horizontal plane-   512 to 515 dimension of plate-   516, 521, 522 distance-   517 A-A cross-sectional view-   518 B-B cross-sectional view-   540 to 544 point group-   801 to 803 vehicle

1. A front monitoring system comprising: an external sensor that ismounted inside a vehicle, emits an exit wave toward a front of thevehicle, and acquires a reflected wave entering the external sensor as adetection signal; and a removing means that removes the exit waveemitted by the external sensor and incident on a structural objectinstalled inside the vehicle in a specific direction.
 2. The frontmonitoring system according to claim 1, wherein the removing meansremoves the exit wave emitted by the external sensor and entering thestructural object at an incident angle larger than a predeterminedangle.
 3. The front monitoring system according to claim 2, wherein theexternal sensor includes a first external sensor and a second externalsensor, and the external sensor that emits the exit wave to be removedby the removing means is the first external sensor or the secondexternal sensor.
 4. The front monitoring system according to claim 3,wherein a plate is used as the removing means, and the plate is disposedbetween the structural object and the first and second external sensors,is located on a front surface side of the first external sensor, a frontsurface side of the second external sensor, or a side surface sidebetween the first and second external sensors, and blocks the exit waveemitted from the first or second external sensor and entering at anincident angle larger than the predetermined angle, thereby removing theexit wave reflected by the structural object and entering the second orfirst external sensor.
 5. The front monitoring system according to claim4, wherein the plate provided on the front surface side of the firstexternal sensor or the front surface side of the second external sensorhas a shape that blocks the exit wave reflecting the structural objectin a horizontal direction and a vertical direction.
 6. The frontmonitoring system according to claim 4, wherein when the plate isprovided on the side surface side between the first external sensor andthe second external sensor, the first external sensor, a firstreflection point in which a reflection point in the structural object ofthe exit wave that is emitted from the first external sensor, reflectedby the structural object, and reaches the second external sensor isclosest to the second external sensor, the plate, a second reflectionpoint in which a reflection point in the structural object of the exitwave that is emitted from the second external sensor, reflected by thestructural object, and reaches the first external sensor is closest tothe first external sensor, and the second external sensor are arrangedin order from the first external sensor toward the second externalsensor.
 7. The front monitoring system according to claim 6, wherein theplate is disposed at an arbitrary position between the first reflectionpoint and the second reflection point, and the plate has a dimensionsatisfying to block the exit wave emitted from the first externalsensor, reflected by the structural object, and incident on the secondexternal sensor and the exit wave emitted from the second externalsensor, reflected by the structural object, and incident on the firstexternal sensor.
 8. The front monitoring system according to claim 3,wherein the removing means is configured by software executed by aprocessing device included in the front monitoring system, and thesoftware includes: a first step of acquiring the detection signal fromthe first or second external sensor that has emitted the exit wave; anda second step of excluding, from the detection signal acquired in thefirst step, the detection signal incident on the second or firstexternal sensor at larger than or equal to a minimum incident angle thatis a minimum value of an incident angle when the exit wave is reflectedby the structural object and is incident on the second or first externalsensor, and holding the detection signal incident on the second or firstexternal sensor at an angle smaller than the minimum incident angle. 9.The front monitoring system according to claim 8, wherein the minimumincident angle is calculated based on at least geometric arrangement ofthe first external sensor, the second external sensor, and thestructural object.
 10. The front monitoring system according to claim 8,wherein the software includes a third step of excluding, from thedetection signal excluded in the second step, the detection signalincident on the second or first external sensor at smaller than or equalto a maximum incident angle that is a maximum value of an incident anglewhen the exit wave is reflected by the structural object and is incidenton the second or first external sensor, as it is, and holding thedetection signal incident on the second or first external sensor at anincident angle larger than the maximum incident angle.
 11. The frontmonitoring system according to claim 10, wherein the maximum incidentangle is calculated based on at least geometric arrangement of the firstexternal sensor, the second external sensor, and the structural object.12. The front monitoring system according to claim 3, wherein theremoving means is configured by software executed by a processing deviceincluded in the front monitoring system, and the software includes: afirst step of acquiring a first detection signal from the second orfirst external sensor in a case where the first or second externalsensor is emitting the exit wave; a second step of acquiring a seconddetection signal from the second or first external sensor in a casewhere the first or second external sensor is not emitting the exit wave;a third step of calculating a third detection signal by excluding thesecond detection signal from the first detection signal; a fourth stepof calculating, from the third detection signal, a minimum incidentangle that is a minimum value of an incident angle of the exit waveincident on the second or first external sensor, and a maximum incidentangle that is a maximum value of an incident angle of the exit waveincident on the second or first external sensor; and a fifth step ofexcluding, from the first detection signal, the first detection signalincident on the second or first external sensor at an incident angle oflarger than or equal to the minimum incident angle and smaller than orequal to the maximum incident angle, and outputting the first detectionsignal.
 13. The front monitoring system according to claim 12, whereinthe first external sensor, the second external sensor, and thestructural object are mounted on the vehicle and at least one vehicledifferent from the vehicle.
 14. The front monitoring system according toclaim 3, wherein the removing means is configured by software executedby a processing device included in the front monitoring system, and thesoftware includes: a first step of acquiring a first detection signalfrom the second or first external sensor in a case where the first orsecond external sensor is emitting the exit wave; a second step ofacquiring a second detection signal from the second or first externalsensor in a case where the first or second external sensor is notemitting the exit wave; a third step of calculating a third detectionsignal by excluding the second detection signal from the first detectionsignal; a fourth step of calculating a direction in which the exit wavecorresponding to the third detection signal is incident on the second orfirst external sensor as an excluding direction; and a fifth step ofexcluding the first detection signal entering from the excludingdirection from the first detection signal and outputting the firstdetection signal.
 15. A front monitoring system comprising: an externalsensor that is mounted inside a traffic route ground facility, emits anexit wave toward a front of the ground facility, and acquires areflected wave entering the external sensor as a detection signal; and aremoving means that removes the exit wave emitted by the external sensorand incident on a structural object installed inside the ground facilityat an incident angle larger than a predetermined angle.
 16. The frontmonitoring system according to claim 9, wherein the software includes athird step of excluding, from the detection signal excluded in thesecond step, the detection signal incident on the second or firstexternal sensor at smaller than or equal to a maximum incident anglethat is a maximum value of an incident angle when the exit wave isreflected by the structural object and is incident on the second orfirst external sensor, as it is, and holding the detection signalincident on the second or first external sensor at an incident anglelarger than the maximum incident angle.
 17. The front monitoring systemaccording to claim 16, wherein the maximum incident angle is calculatedbased on at least geometric arrangement of the first external sensor,the second external sensor, and the structural object.